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Author: Andrea Gruver

Andrea Gruver is a master's student in the Plant Biology and Conservation program through the Chicago Botanic Garden and Northwestern University. She is interested in native bees in Chicago and how urban areas impact their communities.

The plants you see from your train seat on the Metra Union Pacific North line may help conservation scientists learn about how urban areas impact native bees.

Although most people think of honeybees when they think about bees, there are more than 4,000 native bee species in the United States and 500 species in Illinois alone. Like their honeybee counterparts, native bees are undergoing global declines, making them an important conservation concern. With the growth of urban areas, native bees may be faced with new challenges, yet we don’t know the extent that urban areas impact native bees.

My research at the Chicago Botanic Garden is investigating how urban areas may affect native bees in Chicago. Chicago is an ideal city to study the impact of urbanization on native bees because the intensity of urbanization slowly wanes from the urban core of the city out into the surrounding suburbs.

My research is focused on native bee species in Illinois like these Megachilid(leaf cutter) bees.

Part of that research is about bringing public awareness to the other native bees we have around Chicago.

To explore native bee communities along this urbanization gradient, I have a series of eight sites along Chicago’s Union Pacific North Metra (UP-N) railway. I chose the sites along the rail line because they followed a perfect gradient from very urban to very suburban. I was also drawn to them because most of the vegetation around the sites is unmanaged and composed of similar species.

All of the sites vary in the levels of green space and impervious surface (concrete/buildings) surrounding the sites. Sites near downtown are surrounded by nearly 70 percent impervious surface, while sites near the Chicago Botanic Garden are surrounded by just 15 percent impervious surface.

Studying bees in this area along the Metra line allows us to ask a variety of questions about native bees. For instance: Are there fewer bees in highly urban areas? Are there different bees in natural areas compared to urban areas? Do the bees in highly urban areas have different traits than those in natural areas?

Andrea and an intern collect bees along the Metra line.

This summer, a few interns at the Garden and I have been gathering and sampling bees at each of my eight field sites. To catch the bees, we use two methods. First, we set out fluorescent colored bowls with soapy water that attract and capture the bees. Secondly, we use a butterfly net to capture bees at the site throughout the day. When we are finished sampling, the bees are taken back to the lab at the Garden’s Daniel F. and Ada L. Rice Plant Conservation Science Center and pinned for future study.

In addition to collecting the bees, we also record all of the flowering plants and count how many flowers are blooming at the sites.

Although our days are currently filled with fieldwork and pinning, in the fall we will spend almost all of our time in the lab identifying the bees down to the genus or species level. When we have all of the bees identified, we can then start analyzing the data for my master’s thesis and answer some of the questions we have put forth. We suspect we will see a higher abundance and diversity of bees in sites located in more natural areas with more flowering plants.

My research will help us understand how urban areas are shaping native bee communities and help us determine what landscape features promote native bee diversity in urban environments, some of which can be implemented in urban restoration projects. We also hope that this work will illuminate the amazing diversity of native bees we have here in Chicago.

To most people, the word “pollinator” is synonymous with the word “bee,” but only a fraction of plants are pollinated by bees.

In fact, manydifferent insects and mammals are pollinators—bats, birds, beetles, moths, and more. As part of National Moth Week, we wanted to highlight our work on a very special group of moths: the Sphingidae, or hawkmoths, which pollinate more than 106 plant species in North America alone, and many more around the world.

A newly emerged Hyles lineata hawkmoth

I am a research tech in the Skogen lab. I work with Krissa Skogen, Ph.D., her postdocs Tania Jogesh and Rick Overson, and fellow Garden scientist Jeremie Fant, Ph.D., on a National Science Foundation Dimensions of Biodiversity project entitled, “Landscapes of Linalool: Scent-Mediated Diversification of Flowers and Moths across Western North America.” Our project looks at floral scent and pollination in the evening primrose (Onagraceae) family.

Many species in the evening primrose family are pollinated by the white-lined hawkmoth (Hyles lineata). This pollinator is also an important herbivore! Female moths lay eggs on evening primroses, and their hungry caterpillars feed on the leaves, buds, and flowers. How does scent play a role in attracting hawkmoths? Do moths use it for pollination? Or do they use it to find host plants to lay their eggs? Or maybe both?

Hawkmoth pupae (Hyles lineata)

Hyles lineata eggs on an Oenothera harringtonii plant

From Dr. Skogen’s prior research, we know that floral scent can vary within and between plant populations. For instance, within the species O. harringtonii, some populations produce a scent compound called linalool while others do not. We think that the plants face a signaling dilemma: How do they use floral scent to invite their pollinators and yet avoid getting eaten? If female moths use linalool to lay eggs, then perhaps, in some populations, the plants benefit from not advertising their scent. To test this idea, we needed to conduct behavioral experiments to understand how Hyles perceive floral scent

This summer, along with Victoria Luizzi, a summer REU student from Amherst College, we looked at which plants female moths prefer to lay their eggs on—plants from populations containing linalool, or plants from populations without linalool. To answer this question, we first went to Colorado (where the plants naturally grow) and got plants from two different populations, one population that we know produces linalool and another we know doesn’t. Meanwhile our collaborator, Rob Raguso at Cornell University, sent us hawkmoth pupae and we patiently waited for them to emerge.

When the moths emerged they were placed in mating cages. Once mating occurred, females were transferred to a quonset in the evening that contained four plants from the linalool population and four plants from the non-linalool population. The moths were left overnight so the females had plenty of time to choose where they wanted to lay their eggs. The next morning, Victoria counted the eggs on each plant (which was sometimes hundreds!) to see on which plants the females were choosing to lay their eggs. In addition, we dissected each moth to see how many eggs the female did not lay.

Krissa Skogen moves a moth to its new enclosure in her office

Over the course of the project, 12 females were flown in the quonset. Overall, the moths showed a preference for plants from the population that produces linalool. These data suggest that plants risk inviting foes while advertising to their friends—but we’ll need to collect a lot more data to be certain. Ultimately, both the insects that pollinate flowers as well as the insects that eat them might determine how a flower smells! We hope to continue this study to test our hypothesis further and learn more about how scent influences hawkmoth behavior, and how hawkmoth behavior influences floral scent and other floral traits of the plants they pollinate.